Metrology is the scientific study of measurement.[1] It establishes a common understanding of units, crucial in linking human activities.[2] Modern metrology has its roots in the French Revolution's political motivation to standardise units in France, when a length standard taken from a natural source was proposed. This led to the creation of the decimal-based metric system in 1795, establishing a set of standards for other types of measurements. Several other countries adopted the metric system between 1795 and 1875; to ensure conformity between the countries, the Bureau International des Poids et Mesures (BIPM) was established by the Metre Convention.[3][4] This has evolved into the International System of Units (SI) as a result of a resolution at the 11th Conference Generale des Poids et Mesures (CGPM) in 1960.[5]
Metrology is divided into three basic overlapping activities.[6][7] The first being the definition of units of measurement, second the realisation of these units of measurement in practice, and last traceability, which is linking measurements made in practice to the reference standards. These overlapping activities are used in varying degrees by the three basic sub-fields of Metrology.[6] The sub-fields are scientific or fundamental metrology, which is concerned with the establishment of units of measurement, Applied, technical or industrial metrology, the application of measurement to manufacturing and other processes in society, and Legal metrology, which covers the regulation and statutory requirements for measuring instruments and the methods of measurement.
In each country, a national measurement system (NMS) exists as a network of laboratories, calibration facilities and accreditation bodies which implement and maintain its metrology infrastructure.[8][9] The NMS affects how measurements are made in a country and their recognition by the international community, which has a wide-ranging impact in its society (including economics, energy, environment, health, manufacturing, industry and consumer confidence).[10][11] The effects of metrology on trade and economy are some of the easiest-observed societal impacts. To facilitate fair trade, there must be an agreed-upon system of measurement.[11]
Contents
- 1 History
- 2 Subfields
- 3 Concepts
- 3.1 Definition of units
- 3.2 Realisation of units
- 3.3 Standards
- 3.4
measurement.[1] It establishes a common understanding of units, crucial in linking human activities.[2] Modern metrology has its roots in the French Revolution's political motivation to standardise units in France, when a length standard taken from a natural source was proposed. This led to the creation of the decimal-based metric system in 1795, establishing a set of standards for other types of measurements. Several other countries adopted the metric system between 1795 and 1875; to ensure conformity between the countries, the Bureau International des Poids et Mesures (BIPM) was established by the Metre Convention.[3][4] This has evolved into the International System of Units (SI) as a result of a resolution at the 11th Conference Generale des Poids et Mesures (CGPM) in 1960.[5]
Metrology is divided into three basic overlapping activities.[6][7] The first being the definition of units of measurement, second the realisation of these units of measurement in practice, and last traceability, which is linking measurements made in practice to the reference standards. These overlapping activities are used in varying degrees by the three basic sub-fields of Metrology.[6][7] The first being the definition of units of measurement, second the realisation of these units of measurement in practice, and last traceability, which is linking measurements made in practice to the reference standards. These overlapping activities are used in varying degrees by the three basic sub-fields of Metrology.[6] The sub-fields are scientific or fundamental metrology, which is concerned with the establishment of units of measurement, Applied, technical or industrial metrology, the application of measurement to manufacturing and other processes in society, and Legal metrology, which covers the regulation and statutory requirements for measuring instruments and the methods of measurement.
In each country, a national measurement system (NMS) exists as a network of laboratories, calibration facilities and accreditation bodies which implement and maintain its metrology infrastructure.[8][9] The NMS affects how measurements are made in a country and their recognition by the international community, which has a wide-ranging impact in its society (including economics, energy, environment, health, manufacturing, industry and consumer confidence).[10][11] The effects of metrology on trade and economy are some of the easiest-observed societal impacts. To facilitate fair trade, there must be an agreed-upon system of measurement.[11]
The ability to measure alone is insufficient; standardisation is crucial for measurements to be meaningful.[12] The first record of a permanent standard was in 2900 BC, when the royal Egyptian cubit was carved from black granite.[12] The cubit was decreed to be the length of the Pharaoh's forearm plus the width of his hand, and replica standards were given to builders.[3] The success of a standardised length for the building of the pyramids is indicated by the lengths of their bases differing by no more than 0.05 percent.[12]
Other civilizations produced generally accepted measurement standards, with Roman and Greek architecture based on distinct systems of measurement.[12] The collapse of the empires and the Dark Ages which followed them lost much measurement knowledge and standardisation. Although local systems of measurement were common, comparability was difficult since many local systems were incompatible.[12] England established the Assize of Measures to create standards for length measurements in 1196, and the 1215 Magna Carta included a section for the measurement of wine and beer.[13]
Modern metrology has its roots in the French Revolution. With a political motivation to harmonise units throughout France, a length standard based on a natural source was proposed.[12] In March 1791, the metre was defined.[4] This led to the creation of the decimal-based metric system in 1795, establishing standards for other types of measurements. Several other countries adopted the metric system between 1795 and 1875; to ensure international conformity, the International Bureau of Weights and Measures (French: Bureau International des Poids et Mesures, or BIPM) was established by the Metre Convention.[3][4] Although the BIPM's original mission was to create international standards for units of measurement and relate them to national standards to ensure conformity, its scope has broadened to include electrical and photometric units and ionizing radiation measurement standards.[4] The metric system was modernised in 1960 with the creation of the International System of Units (SI) as a result of a resolution at the 11th General Conference on Weights and Measures (French: Conference Generale des Poids et Mesures, or CGPM).[5]
Subfields
Metrology is defined by the International Bureau of Weights and Measures (BIPM) as "the science of measurement, embracing both experimental and theoretical determinations at any level of uncertainty in any field of science and technology".[14] It establishes a common understanding of units, crucial to human activity.[2] Metrology is a wide reaching field, but can be summarized through three basic activities: the definition of internationally accepted units of measurement, the realisation of these units of measurement in practice, and the application of chains of traceability (linking measurements to reference standards).[2][6] These concepts apply in different degrees to metrology's three main fields: scientific metrology; applied, technical or industrial metrology, and legal metrology.[6]
Scientific metrology
Scientific metrology is concerned with the establishment of units of measurement, the development of new measurement methods, the realisation of measurement standards, and
Other civilizations produced generally accepted measurement standards, with Roman and Greek architecture based on distinct systems of measurement.[12] The collapse of the empires and the Dark Ages which followed them lost much measurement knowledge and standardisation. Although local systems of measurement were common, comparability was difficult since many local systems were incompatible.[12] England established the Assize of Measures to create standards for length measurements in 1196, and the 1215 Magna Carta included a section for the measurement of wine and beer.[13]
Modern metrology has its roots in the French Revolution. With a political motivation to harmonise units throughout France, a length standard based on a natural source was proposed.[12] In March 1791, the metre was defined.[4] This led to the creation of the decimal-based metric system in 1795, establishing standards for other types of measurements. Several other countries adopted the metric system between 1795 and 1875; to ensure international conformity, the International Bureau of Weights and Measures (French: Bureau International des Poids et Mesures, or BIPM) was established by the Metre Convention.[3][4] Although the BIPM's original mission was to create international standards for units of measurement and relate them to national standards to ensure conformity, its scope has broadened to include electrical and photometric units and ionizing radiation measurement standards.[4] The metric system was modernised in 1960 with the creation of the International System of Units (SI) as a result of a resolution at the 11th General Conference on Weights and Measures (French: Conference Generale des Poids et Mesures, or CGPM).[5]
Metrology is defined by the International Bureau of Weights and Measures (BIPM) as "the science of measurement, embracing both experimental and theoretical determinations at any level of uncertainty in any field of science and technology".[14] It establishes a common understanding of units, crucial to human activity.[2] Metrology is a wide reaching field, but can be summarized through three basic activities: the definition of internationally accepted units of measurement, the realisation of these units of measurement in practice, and the application of chains of traceability (linking measurements to reference standards).[2][6] These concepts apply in different degrees to metrology's three main fields: scientific metrology; applied, technical or industrial metrology, and legal metrology.[6]
Scientific metrology
Legal metrology "concerns activities which result from statutory requirements and concern measurement, Legal metrology "concerns activities which result from statutory requirements and concern measurement, units of measurement, measuring instruments and methods of measurement and which are performed by competent bodies".[20] Such statutory requirements may arise from the need for protection of health, public safety, the environment, enabling taxation, protection of consumers and fair trade. The International Organization for Legal Metrology (OIML) was established to assist in harmonising regulations across national boundaries to ensure that legal requirements do not inhibit trade.[21] This harmonisation ensures that certification of measuring devices in one country is compatible with another country's certification process, allowing the trade of the measuring devices and the products that rely on them. WELMEC was established in 1990 to promote cooperation in the field of legal metrology in the European Union and among European Free Trade Association (EFTA) member states.[22] In the United States legal metrology is under the authority of the Office of Weights and Measures of National Institute of Standards and Technology (NIST), enforced by the individual states.[21]
Concepts
The realisation of a unit of measure is its conversion into reality.[33] Three possible methods of realisation are defined by the international vocabulary of metrology (VIM): a physical realisation of the unit from its definition, a highly-reproducible measurement as a reproduction of the definition (such as the quantum Hall effect for the ohm), and the use of a material obje
By defining SI base units with respect to physical constants, and not on artifacts or specific substances, they are realisable with a higher level of precision and reproducibility.[30] With the redefinition of the SI units occurring on May 20th, 2019 the kilogram, ampere, kelvin, and mole are now defined by setting exact numerical values for the Planck constant (h), the elementary electric charge (e), the Boltzmann constant (k), and the Avogadro constant (NA), respectively. The second, metre, and candela have previously been defined by physical constants (the caesium standard (ΔνCs), the speed of light (c), and the luminous efficacy of 540×1012 Hz visible light radiation (Kcd)), subject to correction to their present definitions. The new definitions aim to improve the SI without changing the size of any units, thus ensuring continuity with existing measurements.[31][32]
The realisation of a unit of measure is its conversion into reality.[33] Three possible methods of realisation are defined by the international vocabulary of metrology (VIM): a physical realisation of the unit from its definition, a highly-reproducible measurement as a reproduction of the definition (such as the quantum Hall effect for the ohm), and the use of a material object as the measurement standard.[34]
Standards
A standard (or etalon) is an object, system, or experiment with a defined relationship to a unit of measurement of a physical quantity.[35] Standards are the fundamental reference for a system of weights and measures by realising, preserving, or reproducing a unit against which measuring devices can be compared.[2] There are three levels of standards in the hierarchy of metrology: primary, secondary, and working standards.[19] Primary standards (the highest quality) do not reference any other standards. Secondary standards are calibrated with reference to a primary standa
A standard (or etalon) is an object, system, or experiment with a defined relationship to a unit of measurement of a physical quantity.[35] Standards are the fundamental reference for a system of weights and measures by realising, preserving, or reproducing a unit against which measuring devices can be compared.[2] There are three levels of standards in the hierarchy of metrology: primary, secondary, and working standards.[19] Primary standards (the highest quality) do not reference any other standards. Secondary standards are calibrated with reference to a primary standard. Working standards, used to calibrate (or check) measuring instruments or other material measures, are calibrated with respect to secondary standards. The hierarchy preserves the quality of the higher standards.[19] An example of a standard would be gauge blocks for length. A gauge block is a block of metal or ceramic with two opposing faces ground precisely flat and parallel, a precise distance apart.[36] The length of the path of light in vacuum during a time interval of 1/299,792,458 of a second is embodied in an artefact standard such as a gauge block; this gauge block is then a primary standard which can be used to calibrate secondary standards through mechanical comparators.[37]
Traceability and calibration
Several international organizations maintain and standardise metrology.
Metre Convention
The Metre Convention created three main Metre Convention
The Metre Convention created three main international organizations to facilitate standardisation of weights and measures. The first, the General Conference on Weights and Measures (CGPM), provided a forum for representatives of member states. The second, the International Committee for Weights and Measures (CIPM), was an advisory committee of metrologists of high standing. The third, the International Bureau of Weights and Measures (BIPM), provided secretarial and laboratory facilities for the CGPM and CIPM.[42]
General Conference on Weights and Measures
International Bureau of Weights and Measures (French: Bureau international des poids et mesures, or BIPM) is an organisation based in Sèvres, France which has custody of the international prototype of the kilogram, provides metrology services for the CGPM and CIPM, houses the secretariat for the organisations and hosts their meetings.[50][51] Over the years, prototypes of the metre and of the kilogram have been returned to BIPM headquarters for recalibration.[51] The BIPM director is an ex officio member of the CIPM and a member of all consultative committees.[52]International Organization of Legal Metrology
The International Organization of Legal Metrology (French: Organisation Internationale de Métrologie Légale, or OIML), is an intergovernmental organization created in 1955 to promote the global harmonisation of the legal metrology procedures facilitating international trade.[53] This harmonisation of technical requirements, test procedures and test-report formats ensure confidence i
The International Organization of Legal Metrology (French: Organisation Internationale de Métrologie Légale, or OIML), is an intergovernmental organization created in 1955 to promote the global harmonisation of the legal metrology procedures facilitating international trade.[53] This harmonisation of technical requirements, test procedures and test-report formats ensure confidence in measurements for trade and reduces the costs of discrepancies and measurement duplication.[54] The OIML publishes a number of international reports in four categories:[54]
- Recommendations: Model regulations to establish metrological characteristics and conformity of measuring instruments
- Informative documents: To harmonise legal metrology
- Guidelines for the application of legal metrology
- Basic publications: Definitions of the operating rules of the OIML structure and system
Although the OIML has no legal authority to impose its r
Although the OIML has no legal authority to impose its recommendations and guidelines on its member countries, it provides a standardised legal framework for those countries to assist the development of appropriate, harmonised legislation for certification and calibration.[54] OIML provides a mutual acceptance arrangement (MAA) for measuring instruments that are subject to legal metrological control, which upon approval allows the evaluation and test reports of the instrument to be accepted in all participating countries.[55] Issuing participants in the agreement issue MAA Type Evaulation Reports of MAA Certificates upon demonstration of compliance with ISO/IEC 17065 and a peer evaluation system to determine competency.[55] This ensures that certification of measuring devices in one country is compatible with the certification process in other participating countries, allowing the trade of the measuring devices and the products that rely on them.
International Laboratory Accreditation Cooperation
The Joint Committee for Guides in Metrology (JCGM) is a committee which created and maintains two metrology guides: Guide to the expression of uncertainty in measurement (GUM)[59] and International vocabulary of metrology – basic and general concepts and associated terms (VIM).[38] The JCGM is a collaboration of eight partner organisations:[60]
- International Bureau of Weights and Measures (BIPM)
- International Electrotechnical Commission (IEC)
- [61] Each member organization appoints one representative and up to two experts to attend each meeting, and may appoint up to three experts for each working group.[60]
National infrastructure
A national measurement system (NMS) is a network of laboratories, calibration facilities and accreditation bodies which implement and maintain a country's measurement infrastructure.[8][9] The NMS sets measurement standards, ensuring the accuracy, consistency, comparability, and reliability of measurements made in the country.[62] The measurements of member countries of the CIPM Mutual Recognition Arrangement (CIPM MRA), an agreement of national metrology institutes, are recognized by other member countries.[8][9] The NMS sets measurement standards, ensuring the accuracy, consistency, comparability, and reliability of measurements made in the country.[62] The measurements of member countries of the CIPM Mutual Recognition Arrangement (CIPM MRA), an agreement of national metrology institutes, are recognized by other member countries.[2] As of March 2018, there are 102 signatories of the CIPM MRA, consisting of 58 member states, 40 associate states, and 4 international organizations.[63]
Metrology institutes
Calibration laboratories are generally responsible for calibrations of industrial instrumentation.[9] Calibration laboratories are accredited and provide calibration services to industry firms, which provides a traceability link back to the national metrology institute. Since the calibration laboratories are accredited, they give companies a traceability link to national metrology standards.[2] Examples of calibration laboratories would be ICL Calibration Laboratories,[69] Testo Industrial Services GmbH,[70] and Transcat.[71]
[9] Calibration laboratories are accredited and provide calibration services to industry firms, which provides a traceability link back to the national metrology institute. Since the calibration laboratories are accredited, they give companies a traceability link to national metrology standards.[2] Examples of calibration laboratories would be ICL Calibration Laboratories,[69] Testo Industrial Services GmbH,[70] and Transcat.[71]
Accreditation bodies
An organi
An organisation is accredited when an authoritative body determines, by assessing the organisation's personnel and management systems, that it is competent to provide its services.[9] For international recognition, a country's accreditation body must comply with international requirements and is generally the product of international and regional cooperation.[9] A laboratory is evaluated according to international standards such as ISO/IEC 17025 general requirements for the competence of testing and calibration laboratories.[2] To ensure objective and technically-credible accreditation, the bodies are independent of other national measurement system institutions.[9] The National Association of Testing Authorities[72] in Australia, the United Kingdom Accreditation Service,[73] and National Accreditation Board for Testing and Calibration Laboratories[74] in India, are examples of accreditation bodies.
ImpactsMetrology has wide-ranging impacts on a number of sectors, including economics, energy, the environment, health, manufacturing, industry, and consumer confidence.[10][11] The effects of metrology on trade and the economy are two of its most-apparent societal impacts. To facilitate fair and accurate trade between countries, there must be an agreed-upon system of measurement.[11] Accurate measurement and regulation of water, fuel, food, and electricity are critical for consumer protection and promote the flow of goods and services between trading partners.[75] A common measurement system and quality standards benefit consumer and producer; production at a common standard reduces cost and consumer risk, ensuring that the product meets consumer needs.[11] Transaction costs are reduced through an increased economy of scale. Several studies have indicated that increased standardisation in measurement has a positive impact on GDP. In the United Kingdom, an estimated 28.4 percent of GDP growth from 1921 to 2013 was the result of standardisation; in Canada between 1981 and 2004 an estimated nine percent of GDP growth was standardisation-related, and in Germany the annual economic benefit of standardisation is an estimated 0.72% of GDP.[11]
Legal metrology has reduced accidental deaths and injuries with measuring devices, such as radar guns and breathalyzers, by improving their efficiency and reliability.radar guns and breathalyzers, by improving their efficiency and reliability.[75] Measuring the human body is challenging, with poor repeatability and reproducibility, and advances in metrology help develop new techniques to improve health care and reduce costs.[76] Environmental policy is based on research data, and accurate measurements are important for assessing climate change and environmental regulation.[77] Aside from regulation, metrology is essential in supporting innovation, the ability to measure provides a technical infrastructure and tools that can then be used to pursue further innovation. By providing a technical platform which new ideas can be built upon, easily demonstrated, and shared, measurement standards allow new ideas to be explored and expanded upon.[11]
